1. Field of the Invention
The invention relates to a diaphragm dosing, metering or proportioning pump having a dosing chamber, which is provided with an inlet and a pressure-side outlet, as well as a dosing diaphragm operated by a stroke drive, and having a delivery chamber upstream of the dosing chamber and which is provided with a suction connection for the medium to be dosed and a pressure connection, as well as a delivery diaphragm operated by a stroke drive.
2. Description of the Prior Art
Such dosing pumps are more particularly used where it is necessary to reproducibly deliver and supply in dosed manner a liquid medium in small or medium quantities, e.g. in the chemical or pharmaceutical industry, in water treatment and purification plants of different types.
Such diaphragm dosing pumps are in many cases required to have a high dosing precision, even in the case of very small dosed quantities, but this is difficult to achieve. This more particularly applies with liquids, which have a high vapor pressure and/or contain dissolved gases. As a result of the suction pressure, during delivery vapor formation or degassing occurs. As a result of the gases entering the dosing chamber the degree of filling is reduced, so that the dosing precision is significantly lessened.
Another problem occurs in the control of the dosing, because in particular with small or very small dosing quantities conventional flowmeters, e.g. rotating meters and the like, operate too imprecisely as a result of the nonsteady flow caused by the diaphragm stroke and the measurement signals supplied by them are unsuitable for the readjustment of the pump.
U.S. Pat. No. 2,826,067 discloses a control device for a pump delivering from a storage tank. An additional measuring cylinder is connected to the tank, which has measuring devices for determining the volume delivered per time unit. By alignment with a nominal value it is possible to control the pump rate in operation. Due to the hydraulic connection between the tank and the measuring cylinder e.g. constructed as a level gauge and for avoiding an excessive suction pressure, the storage tank must be positioned above the pump, which greatly restricts the range of uses of this construction.
A similar arrangement is disclosed in U.S. Pat. No. 4,897,797. The delivery rate is controlled so that a number of pump strokes determined in a calibration test, during which the liquid level in the measuring cylinder is lowered by a level fixed by two sensors, is compared with the number of strokes actually necessary for this reduction. Also in the case of U.S. Pat. No. 4,897,797, the aforementioned constructional and delivery disadvantages arise as a result of the pump filling fan dependent on the suction head.
German Patent 42 19 664 A1, discloses a diaphragm dosing pump, having an associated auxiliary pump constructed as a diaphragm pump end with which the actual working or dosing chamber of the diaphragm dosing pump is filled independently of the suction head under pressure. The delivery diaphragm of this auxiliary pump is connected to the lifting rod operating the dosing diaphragm. A self-venting valve is provided for the discharge of the gas volumes formed during delivery in the dosing chamber of the diaphragm dosing pump.
In this constructionally complicated apparatus, there is admittedly a filling and venting of the dosing chamber independent of the suction head, but on the one hand the flow measurement for the precise control of dosing is problematical as a result of the nonsteady flow and on the other liquid losses arise due to the vent valve, which leads to relevant errors particularly with very small dosing quantities.